Macrophage colony stimulating factor (CSF-1) is essential for tooth matrix formation and eruption. Ameloblasts and odontoblasts express soluble (s) and cell-surface (cs) forms of CSF-1;however, the precise biologic effects of these isoforms on amelogenesis and the regulatory elements in the CSF-1 gene that control their expression during tooth development have not been explored. The long-term goal of this proposal is to characterize the molecular mechanisms that control CSF- 1 expression in ameloblast lineage cells and determine the biologic effect of CSF-1 isoforms on enamel matrix formation using animal models. Our central working hypothesis is that CSF-1 is critical for amelogenesis during tooth development. Preliminary data show, for the first time, that a -774/+183 bp fragment of the CSF-1 promoter in transgenic mice confers high lacZ expression in the inner enamel epithelial (IEE) cells that differentiate into ameloblasts. Our first hypothesis is that cell-specific cis-acting elements in the -774 bp CSF-1 promoter direct gene expression in ameloblast lineage cells during tooth development. To address this issue, a series of -774 bp ]5'CSF-1 promoter deletion constructs will be tested for transcriptional activity in cultured ameloblast and non-ameloblast cells and relevant sequences will be analyzed in vivo by generating transgenic mice harboring these sequences linked to the lacZ reporter gene. In recent studies using op/op mice that lack both CSF-1 isoforms, we showed that absence of CSF-1 alters tooth matrix protein expression that, in turn, leads to enamel and dentin defects. Transgenic op/op mice expressing either csCSF-1 (op/opCS) or sCSF-1 (op/opS) in odontoblasts under the control of the osteocalcin (OC) promoter were generated and showed distinct tooth phenotypes. sCSF-1 corrected dentin and led to partial correction of enamel defects with op/opS mice showing unique features characterized by chalky white teeth and impaired root formation. These findings are novel and indicate that absence of CSF-1 in ameloblasts of op/opS teeth alters enamel matrix and root development. This is supported by our preliminary data in op/opS mice showing decreased enamelin and kallikrein-4 (KLK4, known as EMSP1) as well as shortened roots. Our second hypothesis is that CSF-1 isoforms differentially regulate enamel matrix and root formation and result in distinct phenotypes. For these experiments, the -774/+183 bp CSF-1 promoter will be used to selectively express sCSF-1 or csCSF-1 in ameloblasts. Double transgenic op/op mice carrying sCSF-1 under the OC promoter and harboring either sCSF-1 or csCSF-1 under the -774/+183 bp promoter will be established. Mice will be examined for resolution of enamel defects and teeth will be analyzed for morphology, enamel matrix protein expression, enamel integrity and mineralization. We will also test the hypothesis that lentiviral-mediated gene delivery of sCSF-1 to ameloblasts will rescue enamel/root defects in op/opS mice. Results from these studies should increase our understanding of the molecular mechanisms that regulate CSF-1 and identify distinct functional effects of sCSF-1 and csCSF-1 that may have therapeutic application for preventing enamel defects in acquired and genetic dental disorders such as amelogenesis imperfecta. PUBLIC HEALTH RELEVANCE: Macrophage colony stimulating factor (CSF-1) is a key regulatory molecule for tooth matrix formation and eruption. Work in this proposal plans to determine the biologic effect of soluble and cell surface forms of CSF-1 on enamel matrix formation and the molecular mechanisms that control CSF-1 expression during tooth development using animal models and gene therapy approaches. Results from these studies may suggest novel therapeutic strategies for enhancing enamel integrity and improving oral health in acquired and genetic dental disorders.